(i) Field of the Invention
The present invention relates to a process for producing a toner for the development of an electrostatic image. More specifically, it relates to a process for producing a toner for the development of an electrostatic image which comprises subjecting a mixture of a high-molecular polymer, a pigment, a dye and a vinyl monomer to suspension polymerization.
(ii) Description of the Related Art
In electrostatic photography, fixing is carried out after an electrostatic image has been developed with a toner, but in general, a toner image is first obtained by developing an electrostatic image retained on a photoconductive photoreceptor or an electrostatic recorder, and the fixing is then carried out by transferring the thus obtained toner image from the photoconductive photoreceptor or the electrostatic recorder to a transfer sheet such as a paper, and then fusing the toner image thereon. In this case, the fusing of the toner image is usually accomplished by bringing the toner image into contact with a solvent vapor or by heating the toner image. In particular, a non-contact heating system using an electric furnace and a pressure heating system using a heating roller are usually employed.
In the pressure heating system using the heating roller, the surface of the heating roller comes in contact with the image on the sheet to be fixed under pressure, and so, in the case that the toner image is thermally fused on the sheet to be fixed, a thermal efficiency is high and the fixing can be carried out rapidly. Therefore, this pressure heating system is extremely suitable for an electrophotographic copying machine. In this system, however, the surface of the fixing roller comes into contact with the toner image in a heating/melting state under pressure, and hence a part of the toner image adheres to the surface of the fixing roller and is then transferred thereto. Then, this part is further transferred to the sheet to be fixed to bring about the so-called offset phenomenon, with the result that the sheet to be fixed is soiled sometimes. Accordingly, it is one of essential requirements for the heating roller fixing method to prevent the toner from adhering to the roller surface.
Japanese Patent Application Laid-open No. 60-88003 discloses a preparation method of a resin for a toner which comprises adding a high-molecular weight vinyl polymer emulsion to an aqueous medium containing a nonionic dispersant, and then subjecting the vinyl monomer to suspension polymerization. However, in the case that this resin is used for with the toner, there is a drawback that the nonionic dispersant remains in large quantities, which has a bad influence on electricity resistance.
Japanese Patent Application Laid-open No. 63-178103 discloses a preparation method of a resin for a toner which comprises subjecting a low-molecular weight vinyl polymer to suspension polymerization by the use of a dispersant selected from the group consisting of anionic and nonionic suspension polymerization dispersants in the presence of a high-molecular weight vinyl polymer emulsion in which an anionic water-soluble high-molecular suspension polymerization dispersant (I) is used as an emulsifying agent. However, in the case that this resin is used for the toner, there is a drawback that a fixing lower limit temperature is high. Thus, the toner having lower-temperature fixing properties is desired.
Furthermore, Japanese Patent Application Laid-open No. 59-14747 discloses a toner for the development of an electrostatic image which contains a suspension-polymerized material of styrene or the like as the main component, but in this case, a temperature at which an offset phenomenon occurs is low, which makes the toner impractical.